#include <GL/glut.h>
#include <cstdlib>

/*
In this lab, we will run an OpenGL program which renders the 3D Sierpinski Gasket

  #1
  Run this code as is.  What is rendered?  Click the left mouse button.  What
  happens?


  #2
  Where is the viewing volume set?  What is it?


  #3
  Turn on the Hidden-Surface removal, or z-buffer.  (Hint: Look for the comments, 
  there are three things to change).  Note that this is NOT double-buffering!
*/

typedef GLfloat point3[3];

point3 v[]={ {0.0,0.0,1.0} , {0.0, 0.942809, -0.333333} , 
{-0.816497, -0.471405, -0.3333333} , {0.816497, -0.471405, -0.333333} };


GLint n=1;

void triangle( point3 a , point3 b , point3 c ) {
	glBegin(GL_POLYGON);
		glNormal3fv(a);
		glVertex3fv(a);
		glVertex3fv(b);
		glVertex3fv(c);
	glEnd();
}

void divide_triangle( point3 a, point3 b , point3 c, GLint m)
{
	point3 v1, v2, v3;
	int j;
	if (m>0)
	{
		for (j=0;j<3;j++) v1[j]=(a[j]+b[j])/2;
		for (j=0;j<3;j++) v2[j]=(a[j]+c[j])/2;
		for (j=0;j<3;j++) v3[j]=(b[j]+c[j])/2;
		divide_triangle(a,v1,v2,m-1);
		divide_triangle(c,v2,v3,m-1);
		divide_triangle(b,v3,v1,m-1);
	} else {
		triangle(a,b,c);
	}
}

void tetrahedron( GLint m )
{
	glColor3f(1,0,0);
	divide_triangle(v[0],v[1],v[2],m);
	
	glColor3f(0,1,0);
	divide_triangle(v[3],v[2],v[1],m);
	
	glColor3f(0,0,1);
	divide_triangle(v[0],v[3],v[1],m);
	
	glColor3f(0,0,0);
	divide_triangle(v[0],v[2],v[3],m);
}

void display ()
{
//	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	tetrahedron(n);
	glFlush();
}

void mouse (int btn, int state , int x, int y)
{
	if (btn==GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
		n++;
		display();
	}
	if (btn==GLUT_RIGHT_BUTTON && state==GLUT_DOWN) {
		exit(0);
	}
}

int main (int argc, char **argv)
{
	glutInit(&argc,argv);
//	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );
	glutInitWindowSize(500,500);
	glutCreateWindow("3D Gasket");
	glutDisplayFunc(display);
	glClearColor(1,1,1,0);
//	glEnable(GL_DEPTH_TEST);
	glutMouseFunc(mouse);
	glutMainLoop();

	return 0;
}